Data Acknowledgement Apparatus and Method

1. A relay node for transmitting data in a network, the network comprising the relay node, a sending node and a receiving node, the receiving node and the relay node being configured to receive data via the network at a first protocol layer and a second protocol layer of a protocol layer stack, the first protocol layer being for transmitting data between adjacent nodes of a connection and the second layer being for establishing a connection in respect of the data, and to send different types of notifications identifying receipt of data, the different types of notifications including: a first type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent; and a second type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent and at the second protocol layer of the receiving node, the relay node comprising: an interface for receiving data at the first protocol layer of the relay node, the data having been sent from the sending node, wherein the interface is configured to send the data to the receiving node; and means for monitoring for a given notification of the second type from the receiving node, wherein the relay node is configured to: cease the monitoring and send, to the sending node, a notification of the second type, in response to receiving the given notification; and send, to the sending node, a notification of the first type, in response to a predefined period elapsing without receipt, at the relay node, of the given notification.

2. The relay node according to claim 1 , wherein the relay node comprises a memory for storing the data and configured to remove the data from the memory in response to receiving the given notification.

3. The relay node according to claim 1 , wherein the relay node is configured to: send, in response to receipt of the given notification at the receiving node after the predetermined time limit has elapsed, a third type of notification, different to the first and second types of notification, the third type of notification identifying receipt of data at the second protocol layer of the receiving node; monitor for a confirmation of receipt of the third type of notification at the sending node; and resend the third type of notification in response to not receiving the confirmation.

4. The relay node according to claim 1 , wherein each of the notifications comprises an identifier of the data.

5. The relay node according to claim 1 , wherein the interface comprises a plurality of interfaces, each configured to receive data at one of the protocol layers of the protocol stack.

6. A method of transmitting data in a network, the network comprising a sending node, a relay node and a receiving node, the receiving node and the relay node being configured to receive data via the network at a first protocol layer and a second protocol layer of a protocol layer stack, the first protocol layer being for transmitting data between adjacent nodes of a connection and the second layer being for establishing a connection in respect of the data, and to send different types of notifications identifying receipt of data, the different types of notifications including: a first type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent; a second type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent and at the second protocol layer of the receiving node; and a third type of notification identifying receipt of data at the second protocol layer of the receiving node, the method comprising: receiving data sent from the sending node at the relay node, and sending the data to the receiving node; receiving a notification at the relay node, the notification being for notifying the sending node of receipt of the data at the receiving node; determining whether the notification is of the second type or the third type of notification; in first case that the notification is determined to be of the second type, not sending a confirmation of receipt of the notification at the relay node to the receiving node; in a second case that the notification is determined to be of the third type, sending the confirmation of receipt; in either case, sending a notification for identifying receipt of data at the receiving node to the sending node, and monitoring for a confirmation of the sent notification having been received at the sending node; and resending the sent notification in response to a predetermined time period elapsing prior to receipt of the confirmation of the sent notification having been received at the sending node.

7. The method according to claim 6 , in which the received notification comprises an identifier of a type of notification and the determining comprises using the identifier.

8. The method according to claim 7 , in which the determining comprises comparing the identifier with a predetermined set of identifiers.

9. The method according to claim 8 , in which the predetermined set of identifiers is stored at the relay node.

10. A node adapted to perform the method of claim 6 .

11. A non-transitory computer readable storage medium storing computer readable instructions thereon for execution on a node to implement a method of transmitting data in a network according to claim 6 .

12. A method of transmitting data in a network, the network comprising a sending node, a relay node and a receiving node, the receiving node and the relay node being configured to receive data via the network at a first protocol layer and a second protocol layer of a protocol layer stack, the first protocol layer being for transmitting data between adjacent nodes of a connection and the second layer being for establishing a connection in respect of the data, and to send different types of notifications identifying receipt of data, the different types of notifications including: a first type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent; and a second type of notification identifying receipt of data at the first protocol layer of the node from which the notification is sent and at the second protocol layer of the receiving node, the method comprising: receiving data at the first protocol layer of the relay node, the data having been sent from the sending node, wherein the interface is configured to send the data to the receiving node; and monitoring for a given notification of the second type from the receiving node; ceasing the monitoring and sending, to the sending node, a notification of the second type, in response to receiving the given notification; and sending, to the sending node, a notification of the first type, in response to a predefined period elapsing without receipt, at the relay node, of the given notification.